The chip type fuse has previously been known (for example, see laid-open Japanese patent publication 2008-52989). The chip type fuse includes an under-glass layer formed on an upper surface of an insulative substrate, a pair of thick film electrodes formed on the glass layer, a fuse element of thin film or thick film formed so as to connect to the thick film electrodes, an over-glass layer formed on the fuse element, and a resin protective layer formed on an upper surface of the glass layer.
Within such a chip type fuse, because the fuse element is covered by under and over glass layers, an effect that heat from the fuse element is stored therein is caused, and the fuse element can be fused with a small overcurrent at high speed.
In the chip type fuse, the fuse element is covered by the glass layers on both sides for improving fusing characteristics based on an assumption of reaction with dry gaseous oxygen in the atmosphere. However, under a high humidity environment, there is a problem that boric oxide of the glass element becomes boric acid, which in turn melts on the fuse element, thereby corroding the fuse element pattern of Cu. Additionally, because the fuse element pattern is formed by Cu on its surface, movement of Cu is promoted when exposed to a high temperature environment, which may result in upheaval of Cu along a grain boundary. Thus there is a possibility that the fuse element may be damaged by long term use in a high humidity and/or high temperature environment.